Direct-positive silver halide emulsions containing gold salt complex addenda

ABSTRACT

GOLD SALT COMPLEXES CAN BE ADDED TO FOGGED, DIRECTPOSITIVE SILVER HALIDE EMULSIONS TO IMPROVE THEIR PHOTOGRAPHIC PROPERTIES, ESPECIALLY THE MAXIMUM DENSITY UPON AGING. PREFERABLY, THE EMULSIONS OF THIS INVENTION CONTAIN REDUCTION AND GOLD FOGGED SILVER HALIDE GRAINS.

United States Patent Oflice 3,672,903 Patented June 27, 1972 3,672,903 DIRECT-POSITIVE SILVER HALIDE EMULSIONS CONTAINING GOLD SALT COMPLEX ADDENDA Elizabeth Puiiu Chang, Webster, N.Y., assignor to Eastman Kodak Company, Rochester, N.Y. No Drawing. Filed Feb. 16, 1970, Ser. No. 11,837 Int. Cl. G03c 1/28, 1/30 U.S. Cl. 96-108 12 Claims ABSTRACT OF THE DISCLOSURE Gold salt complexes can be added to fogged, directpositive silver halide emulsions to improve their photographic properties, especially the maximum density upon aging. Preferably, the emulsions of this invention contain reduction and gold fogged silver halide grains.

This invention relates to direct-positive photographic silver halide emulsions. In one aspect, this invention relates to the addition of gold complexes as an addendum after the fogging of a direct-positive silver halide emulsion to improve the photographic properties of said emulsion. In another aspect, this invention relates to directpositi-ve halide emulsions which have improved maximum image density upon incubation and aging.

It is known in the art that different types and degrees of chemical fogging will provide variations in maximum density produced upon development. Moreover, the maximum density obtained with various fogging agents varies with age and keeping conditions of the fogged emulsions. In one particular instance, reduction and gold fogged direct-positive silver halide emulsions have high maximum density upon development of fresh samples, but it falls off with age and keeping conditions. When higher concentrations of gold salt are used in the fogging step, the maximum density upon aging is somewhat stabilized, but the photographic speed decreases. It is desirable to provide new approaches to obtain a fogged direct-positive system with improved aging properties and improved photographic properties.

I have now found that the photographic properties of a fogged direct-positive silver halide emulsion, and especially the maximum density stability, can be improved by the addition of gold complexes to the gelatin used to make up the coating emulsion or to the fully sensitized, fogged, direct-positive emulsion. The improvements are especially noticeable in direct-positive silver halide emulsions which have been reduction and gold fogged. Moreover, in certain preferred embodiments wherein the gold complex salts are added within the optimum concentration ranges, the photographic speed of producing the positive image and the shape of the sensitometric curve is substantially the same as a fresh control emulsion without the gold addendum:

In one preferred embodiment, the gold complex is a monovalent gold complex, i.e. where the gold is in the monovalent state.

In a highly preferred embodiment, the gold complex is an alkali metal or ammonium aurous dithiosulfate.

In another preferred embodiment, the gold complex addenda is added to a direct-positive emulsion which has been reduction and gold fogged.

In another preferred embodiment, this invention relates to a process of making a photographic element comprising (1) fogging the silver halide emulsion, (2) adding a gold salt complex to the emulsion and (3) coating said emulsion on a support.

In still another preferred embodiment, the gold complex is added to a fogged, direct-positive silver halide emulsion wherein the grains of said silver halide emulsion contain sites for the formation of phottlytic silver.

In a highly preferred embodiment according to this invention, the gold salt complexes are added to reduction and gold fogged silver halide emulsions to provide very good improvements in photographic properties, especially when an alkali metal or ammonium aurous dithiosulfate is added to the emulsion.

Generally, the gold complexes of this invention can be incorporated into the emulsion at any time after the fogging steps. Preferably, they are added to the fogged, direct-positive emulsion after all ripening, sensitizing and digestion steps are completed in a manner which will substantially avoid immediate reaction with the silver halide. Suitable concentrations of the gold complex are generally from about 1 mg. to about 200 mg. per mole of silver halide and preferably from about 20 to about 60 mg. per mole of silver halide.

Typical useful gold complexes include alkali-metal aurous dithiosulfates, alkali-metal auric halide complexes, aurous sulfide, thiourea-auric halide complexes, auric chloride 3 ethyl-5-[ (3-ethyl-2(3H)-benzoxazolylidene) ethylidene]-rhodanine addition products, alkali-metal auric thiocyanates, 1',1'-diethyl-2,2'-cyanine auric tetrachloride and the like. Preferably the gold complex is an alkali-metal aurous dithiosulfate.

The direct-positive silver halide compositions useful in this invention can be generally classified as blue-sensitivedirect-positive silver halide compositions. It is understood that blue-sensitive means that the direct-positive compositions will provide a reversal image when exposed with light in the 350- to 500-millimicron range of the electromagnetic spectrum and then developed. The silver halide compositions can also be spectrally sensitized so as to form reversal images when exposed in other regions of the spectrum such as in the green and red regions. However, they all have the property of being capable of forming a reversal image when exposed with light in the blue region of the visible spectrum.

Typical direct-positive silver halide compositions useful in the present invention include:

(1) Emulsions containing fogged silver halide grains which have internal centers for the deposition of photolytic silver such as those generally disclosed in Berriman, U.S. Pat. 3,367,778 issued Feb. 6, 1968, including emulsions comprising grains which have centers which promote the deposition of silver which are either sufiiciently small or sufficiently buried within the crystal as to be not accessible to initiate surface development to a visible image. Silver halide grains of this latter type can be provided by '(a) using very low concentrations of sensitizing agent throughout the precipitation, (b) adding the sensitizing agent to the precipitation medium during the initial part of the precipitation, (c) reducing part of the silver nitrate used in the initial portion of the precipitation, etc.

(2) Emulsions which contain silver halide grains which are uniformly fogged to specific levels and contain electron-accepting compounds adjacent the grains, as described in lllingsworth, U.S. Ser. No. 619,948 filed Mar. 2, 1967, now U.S. Pat. 3,501,305 issued Mar. 17, 1970.

(3) Emulsions comprising fogged regular grains which contain an electron-accepting compound or desensitizer adjacent the grains, as described in lllingsworth, U.S. Ser. No. 619,909 filed Mar. 2, 1967, now U.S. Pat. 3,501,306 issued Mar. 17, 1970.

(4) Emulsions comprising monodispersed grains which have been reduction and gold fogged, as described in lllingsworth, U.S. Ser. No. 619,936 filed Mar. 2, 1967, now U.S. 'Pat. 3,501,307 issued Mar. 17, 1970.

(5) Emulsions similar to the above which provide a reversal image when exposed to blue light.

The silver halides employed in the preparation of the photographic compositions described herein include any of the photographic silver halides as exemplified by silver bromide, silver chloride, silver chlorobromide, silver bromoiodide, silver chlorobromide, and the like. Silver halide grains having a mean grain diameter, i.e., an average grain size in the range of about .01 to about 2 microns, preferably about .02 to about 1 micron, give particularly good results in reversal systems. The silver halide grains can be any suitable shape such as cubic or octahedral, but they are preferably cubic, and more preferably cubic-regular. The preferred photographic silver halide emulsions comprise at least 50 mole percent bromide, the most preferred emulsions being silver bromoiodide emulsions, particularly those containing less than about 10 mole percent iodide. The photographic silver halides can be coated at silver coverages in the range of about 50 to about 500 milligrams of silver per square foot of support.

The direct-positive photographic silver halide emulsions of this'invention contain silver halide grains which are fogged. Fogging can be effected by chemically or physically treating the photographic silver halides by methods previously described in the prior art. Such fogging can be accomplished by various techniques such as chemical sensitization to fog, particularly good results being obtained with techniques of the type described by Antoine Hautot and Henri Saubenier in Science et Industries Photographiques vol. XXVIII, January 1957, pages 57- 65.. The silver halide grains can be fogged with the highintensity light, reduction fogged with a reducing agent such as thiourea dioxide or stannous chloride or fogged with gold or noble metal compounds. Combinations of reduction fogging agents with gold compounds or compounds of another metal more electropositive than silver, e.g., rhodium, platinum or iridium, can be used in fogging the silver halide grains. The fogged silver halide grains in the direct-positive photographic emulsions of this invention give a density of at least 0.5 when developed without exposure for minutes at 68 F. in Kodak DK-50 developer when a direct-positive emulsion containing such grains is coated at a coverage of 50 to about 5000 mg. of silver per square foot of support.

The direct-positive photographic emulsions of this invention can comprise reduction and gold fogged silver halide grains, i.e., silver halide grains which are fogged with a combination of a reduction fogging agent and a gold fogging agent. The use of low concentrations of reduction and gold fogging agents in such a combination give unique fogged silver halide grains which are characterized by a rapid loss of fog upon chemical bleaching. It is known that 1 equivalent weight of a reducing agent will reduce 1 equivalent weight of silver halide to silver. To obtain the fogged silver halide grains which are characterized by a rapid loss of fog upon bleaching, much less than 1 equivalent weight of reduction fogging agent is employed. Thus, less than about 0.06 milli-equivalent of reduction fogging agent per mole of silver halide is employed in fogging the silver halide grains. Generally, about 0.0005 to about 0.06, preferably about 0.001 to about 0.03, milliequivalent of reduction fogging agent per mole of silver halide is employed in fogging the silver halide grains in the practice of this invention. Higher concentrations of reduction fogging agent can result in a substantial loss in photographic speed. A preferred reduction fogging agent employed in combination with a gold fogging agent, or a compound of another metal more electropositive than silver, is thiourea dioxide which is preferably employed in a concentration in the range of about 0.05 to about 3, most preferably about 0.1 to about 2 mg. per mole of silver halide or about 0.005 to about 0.03 millimole per mole of silver halide. Stannous chloride is another suitable reduction fogging agent which is used in practicing this invention and is preferably used in concentrations in the range of about 0.05 to about 3 mg. of stannouschloride per mole of silver halide.

The use of the reduction and gold fogging agents in low concentration gives direct-positive photographic silver halide emulsions exhibiting outstanding photographic speed. Examples of suitable reduction fogging agents which can be employed in the practice of this invention include hydrazine, phosphonium salts such as tetra (hydroxy methyl) phosphonium chloride, thiourea dioxide as disclosed in U.S. Pats. 3,062,651 by Hillson issued Nov. 6, 1962, and 2,983,609 by Allen et al. issued May 9, 1961, reducing agents such as the stannous salts, e.g., stannous chloride, as disclosed in U.S. =Pat. 2,487,850 by Carroll issued Nov. 15, 1939, polyamines such as diethyleue triamine as disclosed in U.S. zPat. 2,519,698 by Lowe et al. issued Aug.

15, 1950, polyamines such as spermine as disclosed in U.S.

Pat. 2,521,925 by Lowe et al. issued Sept. 12, 1950, his (fl-aminoethyl) sulfide and its water-soluble salts as disclosed in U.S. Pat. 2,521,926 by Lowe et al. issued Sept. 12, 1950, and the like.

The gold fogging agents employed in practicing this invention can be any gold salt suitable for use in fogging photographic silver halide grains and includes the gold salts disclosed in U.S. Pats. 2,399,083 by Waller et al. issued Apr. 23, 1946, and 2,642,361 by Damschroder et al. issued June 16, 1953. Specific examples of gold fogging agents are potassium chloroaurite, potassium aurithio cyanate, potassium chloroaurate, auric trichloride, 2-aurosulfobenzothiazole metho chloride, and the like. The concentration of gold fogging agent employed in the practice of this invention is subject to variation, but is generally in the range of about 0.001 to about 0.01 millimole per mole of silver halide. Potassium chloroaurate is a preferred gold fogging agent and is often used at concentrations of less than about 5 mg. per mole of silver halide and preferably at concentrations in the range of about 0.5 to about 4 mg. per mole of silver halide.

Preferably, the direct-positive emulsion used in this invention contain electron-accepting compounds, often referred to as a desensitizers or electron traps, which are generally compounds having an anodic polarographic halfware potential and a cathodic polarographic potential which, when added together, give a positive sum. Typical useful electron-accepting compounds, along with methods of determining the polarographic potentials, are disclosed in the above-mentioned applications on direct-positive emulsions, as well as in Illingsworth et al., U.S. Ser. No. 609,761 filed Jan. 17, 1967, now U.S. Pat. 3,- 501,310 issued Mar. 17, 1970. An especially useful class of electron acceptors which can be used in the directpositive photographic silver halide emulsions, and procasses of this invention are cyanine dyes such as the imidazo [4,5-b] quinoxaline dyes. Dyes of this class are described in Brooker and Van Lare, Belgian Pat. 660,253 issued Mar. 15, 1965. 'In these dyes, the imidazo[4,5-b] quinoxaline nucleus is attached, through the Z-carbon atom thereof, to the methine chain.

The direct-positive emulsions of this invention also can contain compounds referred to as halogen-accepting or halogen-conducting compounds, especially if the halide of the emulsion is predominantly chloride. Useful compounds of this type are generally characterized by an anodic polarographic potential less than 0.85 and a cathodic polarographic potential which is more negative than 1.0. Highly preferred species of compounds of this type are merocyanine dyes having the above halfwave potentials. Typical compounds of this type, along with methods of determining the polarographic potential, are disclosed in the above-mentioned applications on direct-positive emulsions as well as in Wise, U.S. Ser. No. 615,360 filed Feb. 13, 1967, now U.S. Pat. 3,537,858 issued Nov. 3, 1970.

The emulsions of this invention can also contain the hardeners, coating aids, surfactants, development modifiers, sensitizers, stabilizers, incorporated developer agents, binder vehicles and lubricants as disclosed in the art for direct-positive emulsions.

6 The improved direct-positive emulsions of this invention Dyes which are used as electrons acceptors in emulsions can be processed by conventional photographic developof this type accelerate the density reduction as described mcnt processes, monobath processes, two-stage processes in Example 2. and the like as generally known in the art for blue-sensi- EXAMPLE 2 tive-direct-positive silver halide emulsions. Typical useful two-stage processes referred to above include those de- In thls example the emulslon 15 the Same as scribed in Bath Rapid Stabilization Processing, The ample 1 with a spectral-sensitizing dye added before the British Journal of Photography, July 21, 1967, pages 620- 3 2 3?2 z f k P fi f T 25; Broughton, U.S. Pat. 2,514,927; British Pat. 1,003,- P 8 dye 1s a v q -qg 436; and Barbier, US. Pat. 3,212,895 issued Oct. 19, 1965. 10 mdolo carbocvanme y of t e type described In Brooker Typical useful monobath processes include Levy, Cornand vanLal'e, 110W Patbined Development and Fixation of Photographic Images The coatlng and Processmg condlfilons are i h h Phot, Sch & Eng VOL 2, 3, Octoidentlcal to those of Example 1. The fresh and incubated b 1953; Barnes et al US p 3 019; and the hka results are listed below and show the advantages of the The invention can be further illustrated by the followaddltlon of the gold complexmg examples.

Relative Mg. Na [Au(Sa)2].2H2O spied at D Percent D Per liter make-up Per mole i m!; 1655?; gelatin Ag Fresh Inc. Fresh Inc. incubation Fresh Inc.

EXAMPLE 1 EXAMPLE 3 Silver bTQmOiOdide gelatin m The emulsion and coating conditions are the same as in duction and gold fogged, 1s prepared as described in 'Berri- Example 2 With the exception that the man, US. 'Pat. 3,367,778, and used to illustrate the in- N [AMS 0 TH O vention. A water solution of gold complex, dd d h h f 3 2 d 2 h is a e to t e emu sion e ore a ding t e spectral-sensi- Naa [Au(s2o3)2] ZHZO tizing dye and make-up gelatin. Exposure and processing is added to the make-up gelatin before coating at various of fresh and incubated coatings as in Example 1 give the concentrations. Additional gelatin is then added to the results as listed below; these results show the advantages chemically fogged emulsion, and the emulsion samples are of the addition of the gold complex seen in Example 2 coated at 100 mg. silver and 250 mg. gelatin/ft. on a wherein the gold complex is added to the make-up gelatin.

Relative Mg. N8:4[A11(S203)2].2H2O speed at Percent DIDBX- DEB! max. mih- Per liter of coating Perrnole loss on melt Ag Fresh Inc. Fresh Inc. incubation Fresh Inc.

cellulose acetate support. The film 1s incubated for 1 EXAMPLE 4 week at 120 F. and relative humidity. The fresh and incubated coatings are exposed on an Eastman 1B sensi- This example is the same as Example 1 except that tometer for 1 second to a 500 w. 3000 K. bulb modulated KAuCl -2H O is used in place of Na [Au(S O -2H O.

Relative Mg. KAIICh-ZHaO speed at Percent m x. Dinnz. Dmax. 1055 Dmln. Per liter of make-up Per mole on incubagelatin Ag Fresh Inc. Fresh Inc. tion Fresh Inc.

by a step wedge, developed 6 minutes in an Elon-hydro- EXAMPLE 5 quinone developer, fixed, washed and dried. Results in the The emulsion and coating conditions are the same as in following table show the advantages of the addition of Example 2. The KAuC1 -2H O is added to the emulsion the addition of the gold complex. before adding the spectral-sensitizing dye and make-up gelatin. The results are listed in the following table.

Relative Mg. Na [Au(SzOa)2].2HzO speed at Percent 2 max. Dmax. Dmnx- Dinin- Per liter make-up Per mole loss on gelatin (4%) Ag Fresh Inc. Fresh Inc. incubation Fresh Inc.

0 76 2. 40 1. 76 26. 6 0. 07 0. O6 0. 234 100 76 2. 40 1. 76 26. 6 0. 07 0. 06 2. 36 91 76 2. 40 1. 82 24. 1 0. 08 0. 06 11. 8 87 2. 50 2. 16 13. 6 0. l0 0. 07 23. 6 76 73 2. 52 2. 40 4. 7 0. 14 0. 1O 47. 1 74 69 2. 56 2. 44 4. 6 0. 20 0. 16 117. 8 76 67 2 50 2. 38 4. 8 0. 30 0. 4O

Relative Mg. KA11C143H3O speed at Percent 36 Diana. mlx. 1211:.1 Drain Per liter of coating Per mole on incuba melt Ag Fresh Inc Fresh Inc. tion Fresh Inc.

EXAMPLE 6 EXAMPLE 7 Dyes I-VII are added with and without 20 mg. of the gold complex Na [Au(S O ),]-2H,O/Ag mole to portions of a reduction and gold fogged silver bromoiodide gelatin emulsion of the type described in Berriman, US. Pat. 3,367,778. The emulsion samples are held for 10 minutes at 40 C., coated on cellulose acetate film support at 100 mg. Ag/ftfi, chill-set and dried. The films are exposed on an Eastman 1B sensitometer to a 500 W. 3000 K. bulb modulated by a step wedge, developed 6 minutes in an Elon-hydroquinone developer, fixed, washed and dried. Another set of coatings is incubated for 1 Week at 120 F./50% RH before exposure and development. Results in the table show that the stability seen by the addition of the gold complex is maintained on spectral While many gold salt complexes provide improved results, the preferred incubation stability is obtained with pounds of US. Pat. 2,597,915 (II and IH) are dissolved in acetone and stirred into the make-up gelatin. The emulsion samples are coated, incubated and tested as in Example 1. Results in the following table show that although the gold compounds of US. Pat. 2,597,915 improve the stability of the emulsion somewhat, there is greater D sensltrzatlon of this emulsion w1th other dye classes. loss on mcubatlon and reduced fresh speed compared to l d D D P t t s l i C ear spee mlx. min. ercen I I 2 COIHL, max. R 6! T I mg./m. Fresh Inc. Fresh Inc. Fresh Inc. loss 500 100 151 1.57 .78 .05 .05 50.3 500 91 151 1. 7a 1. 1s 06 05 31.8 500 100 95 1. 06 .57 .06 .06 65.7 500 78 100 1.76 .88 .07 .06 60.0 500 100 174 1.68 .52 .09 .09 69.0 500 100 195 1. 72 76 10 10 55. s 500 100 141 1.64 .62 .06 .06 62.2 500 87 141 1.70 .89 .06 .06 47.6 500 100 148 1.68 .80 .06 .05 52.4 500 87 141 1. 71 1.08 06 05 36. a 600 100 219 1. 55 .35 11 10 77. 4 500 87 204 1.67 .68 .14 .10 66.3 500 100 182 1. 67 62 10 08 68. 9 500 89 182 1.72 .70 .09 .08 65.8

Norm-Dye I=1,3-dlallyl-6-ehloro-l-methyl-2-phenylimidazo[4,5-b]-quinoxa1ino-3-lndolocarbocyar1ine ptoluenesulionate.

Dye II=1,1 dimethyl-2 2-diphenyl-3,3'-benz[g]indolocarhocyanine bromide.

-trlmethyl-1,3-diphenylimidazo-[4,5-b]quin0xalinoindo0arbocyanin0 iodide.

" Dye IV=1,3-dlally1-1,3 ,3-t1'imethyl-6-nitroimidazo[4,5-b]-quinoxalinoindocarbo0yanine bromide.

Dye V=2-[2-(1,B-diphenyl-Z-pyrrolyl) vinyll-l,3,3-trimethyl-fi-nitro-liH-indolium perchlorate. Dye VI=1,3,3-trimethyl-8,lO-diphenyl-SH-benz0[glimldaz0-[4,5-b]quinoxalinoindocarbocyapme iodide. Dye VII=1,3,3-trimethyl-6-nitro-1,3-diphenyllmidazo[4,5-b]quinoxallnoludocarboeyanine iodide.

optimum concentrations of aurous dithiosulfate used in Example 1.

Mg. gold compound! Relative speed Percent liter Of 81} Dmn. unn. max. Dmu.

make-up loss on gelatin Fresh Inc. Fresh Inc. incubation Fresh 11101;-

i 4. 43 1. 78 1. 58 11. 2 0. 17 0. 09 2. 75 69 120 1. 73 0. 97 43. 9 0. 10 0. 05 III 1 3. 60 182 1. 1. 06 37. 6 0. l2 0. 06

N o'rE.-(l'.) Thiourea gold complex:

5 H7 NH2)4] lz (II) 1], 1'-dietl1yl-2, 2'-eyanine auric tetrachloride:

Although the invention has been described in considerable detail with particular reference to certain preferred embodiments thereof, variations and modifications can be etfected within the spirit and scope of the invention.

I claim:

1. In a direct-positive, fogged silver halide emulsion, the improvement comprising at least about 1 mg. per mole of silver halide in said emulsion of a gold salt complex selected from the group consisting of alkali metal and ammonium aurous dithiosulfates, alkali metal auric halide complexes, thioureaauric halide complexes, auric chloride 3 ethyl--[(3-ethyl-2-(3H)-benzoxazolylidene) ethylidene1-rhodanine addition products, 1,1' diethyl- 2,2'-cyanine auric tetrachloride and alkali metal auric thiocyanates, said gold salt complex being added to said emulsion after fogging the emulsion.

2. An improved direct-positive emulsion according to claim 1 wherein said silver halide emulsion comprises reduction and gold fogged silver halide grains.

3. An improved direct-positive emulsion according to claim 1 wherein said direct-positive silver halide emulsion is blue-sensitive.

4. An improved direct-positive emulsion according to claim 1 wherein said silver halide emulsion comprises fogged grains which have internal centers which promote the deposition of silver.

5. An improved direct-positive emulsion according to claim 1 wherein said silver halide grains are reduction with gold fogged and have adsorbed to the surface thereof an electron-accepting compound which has an anodic polarographic halfwave potential and a cathodic polarographic potential which, when added together, give a positive sum.

6. An improved blue-sensitive-direct-positive silver halide emulsion comprising reduction and gold fogged silver halide grains and having internal sites for the deposition of photolytic silver and/or an electron-accepting compound adsorbed to the surface of said fogged grains, said electron-accepting compound having an anodic polarographic half-wave potential and a cathodic polarognaphic potential which, when added together, give a positive sum, the improvement comprising the addition of at least 1 mg. per mole of silver halide of a gold salt complex to said emulsion after fogging the silver halide grains wherein the gold salt complex is selected from the group consisting of alkali metal and ammonium aurous dithiosulfates, alkali metal auric halide complexes, thiourea-auric halide complexes, auric chloride 3 ethyl-5-[(3-ethyl-2 (3H)-benzoxazolylidene) ethylidene1-rhodanine addition products, l',1'-diethyl 2,2 cyanine auric tetrachloride and alkali metal auric thiocyanates.

7. A process of making a fogged, direct-positive silver halide element comprising the steps of (1) reduction and gold fogging silver halide grains, (2) adding a gold salt complex selected from the group consisting of alkali metal and ammonium aurous dithiosulfates, alkali metal auric halide complexes, thiourea-auric halide complexes, auric chloride 3 ethyl-5-[(3-ethyl-2(3H)-benzoxazolylidene) ethylidene1-rhodanine addition products, l,1'-diethyl-2,2' cyanine auric tetrachloride and alkali metal auric thiocyanates as an addendum, in a concentration of about 1 mg. to about 200 mg. of said complex per mole of silver halide, to an emulsion comprising said fogged grains, and (3) coating the emulsion containing said gold salt complex on a support.

8. A process of making a fogged, direct-positive photographic silver halide element comprising the steps of (1) reduction and gold fogging silver halide grains, (2) adding an ammonium or alkali metal aurous dithiosulfate as an addenum, in a concentration of about 20 to about 60 mg. per mole of silver halide to an emulsion comprising said fogged grains, and (3) coating the emulsion containing said ammonium or alkali metal aurous dithiosulfate on a support.

9. A process of making a fogged, direct-positive, silver halide emulsion comprising the steps of (1) reduction and gold fogging silver halide grains, and (2) adding a gold salt complex selected from the group consisting of alkali metal and ammonium aurous dithiosulfates, alkali metal auric halide complexes, thiourea-auric halide complexes, auric chloride 3 ethyl-5-[(3-ethyl-2(3H)-benzoxazo1ylidene) ethylidene1-rhodanine addition products, 1',l-diethyl-2,2'-cyanine auric tetrachloride and alkali metal auric thiocyanates, as an addendum, in a concentration of about 1 mg. to about 200 mg. of said complex per mole of silver halide, to an emulsion comprising said fogged grams.

10. A process of making a fogged, direct-positive, silver halide emulsion comprising the steps of (1) reduction and gold fogging silver halide grains and (2) adding an ammonium or alkali metal aurous dithiosulfate as an addendum, in a concentration of about 20 to about 60 mg. per mole of silver halide, to an emulsion comprising said fogged grains.

11. In a photographic element comprising a support having thereon a direct-positive, fogged silver halide emulsion, the improvement comprising at least about 1 mg. per mole of silver halide in said emulsion of a gold salt complex selected from the group consisting of alkali metal and ammonium aurous dithiosulfates, alkali metal auric halide complexes, thiourea-auric halide complexes, auric chloride 3 ethyl-5-[(3-ethyl-2(3H)-benzoxazolylidene) ethylidene1-rhodanine addition products, 1',1'-diethyl-2, 2'-cyanine auric tetrachloride and alkali metal auric thiocyanates, said gold salt complex being added to said emulsion after fogging the emulsion.

12. In a photographic element comprising a support having thereon a direct-positive, fogged silver halide emulsion, the improvement comprising about 20 mg. to about 60 mg. per mole of silver halide in said emulsion of an ammonium or alkali metal aurous dithiosulfate which is added to said emulsion after fogging the emulsion.

References Cited UNITED STATES PATENTS 2,597,856 5/ 1952 Damschroder 96108 2,575,002 11/1951 Carroll et al. 96108 3,501,305 5/1970 Illingsworth 96108 FOREIGN PATENTS 723,019 2/ 1955 Great Britain 9664 636,140 4/1950 Great Britain 96110 NORMAN G. TORCHIN, Primary Examiner R. E. FICHTER, Assistant Examiner US. Cl. X.R. 96110 

